A note on the partial likelihood estimator of the proportional hazards model for combined incident and prevalent cohort data

The proportional hazards model has been well studied in the literature for estimating the effect of covariate data on the failure time hazard rate. This model is routinely applied to right-censored incident cohort failure time data as well as left-truncated right-censored failure time data obtained from a prevalent cohort study with follow-up. In a meta-analysis or complex study design, data from both incident cohort and prevalent cohort studies with follow-up may be available. We compare two partial likelihood estimation approaches for the covariate effects using combined incident and prevalent cohort data under the proportional hazards model. We validate the partial likelihood methods through the concept of ancillarity and utilize simulated cohort data to compare the two procedures.